PATCH: XGraphicsConfiguration implement font metrics cache

[Scott Gilbertson]

I have revised the font cache patch in the following ways, and I claim it's
ready to check in.
 - one cache per Display, referenced through a Hashtable
 - when putting the 11th font in any cache, the least-recently-used one is
removed
 - code-wise, the cache is now implemented in an inner class
 - also modified the font name format, which wasn't letting me load certain
fonts

To test it, I reduced the LRU threshold to 4 and added a bunch of println
statements.  I confirmed that fonts were getting cached, found, created and
removed as intended.  I then removed the printlns and bumped the LRU
threshold to 10.

Caveats:
1. Nothing gets disposed, so server resources could be tied up for some time
after discarding a font from the cache.
2. The LRU assessment is based on an integer counter, which will eventually
overflow if you run for a very long time with 10 or fewer fonts, one or more
of which were only used at startup, then suddenly use some new fonts.  If
that happens, I predict that the cache will sometimes discard a few of the
wrong fonts.  Although I haven't tested this scenario, I'm pretty sure it
will be OK, other than a very slight momentary performance hit.
3. There's a lot of hash-tabling, which could be reduced by moving the cache
into Display.  I opted instead, however, to keep the change nicely contained
in XGraphicsConfiguration.
4. If you have more than ten fonts on-screen at once, there might be some
unfortunate overhead.  I think, however, that even in these cases,
performance will be better than it would without a cache.

Index: libjava/ChangeLog
from  Scott Gilbertson  <scottg@mantatest.com>

 * XGraphicsConfiguration.getXFontMetrics:  implemented cache to improve
performance

revised patch is attached.


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